Acousto-optic modulators (AOMs) are often used to split and/or modulate a laser beam. The basic principle of AOMs is that a transparent medium subject to a stress undergoes a change in the index of refraction. When the stress is high frequency sound waves, such as might be produced by a piezoelectric transducer, the change in refraction is periodic. The periodic refraction pattern can act as a diffraction grating producing what is called Bragg diffraction. The undiffracted beam is called the zeroth order beam and the primary diffracted beam is called the first order beam.
Amplitude modulation of laser beams is another requirement for many applications. The amount of light diffracted in an AOM is a function of the acoustic power being applied and can, therefore, be modulated by varying the applied power. Generation of a second modulated beam from one original incident beam using prior art techniques requires a second AOM in series with the first. The second modulated beam created this way may vary significantly from the first modulated beam in intensity or size and may contain an admixture of the modulation characteristics of the first modulated beam.
Many laser applications require the use of beam splitters to derive two equal intensity beams from an original beam. Conventional spatial beam splitting techniques such as partial reflective/transmissive lens coatings can produce two continuous beams of at most approximately 50% intensity. Another disadvantage with conventional beam splitters is that they are not available for all wavelengths. Mechanical splitting or chopping techniques such as rotating polygon mirrors have all of the disadvantages associated with moving parts such as speed variations and limitations.